1. Field of the Invention
The present invention relates to rock bolts suitable for use in the mining and tunnelling industries to provide rock and wall support. The invention is suitable for use in hard rock applications as well as in softer strata, such as that often found in coal mines, and it is to be appreciated the term “rock” as used in the specification is to be given a broad meaning to cover both these applications.
2. Description of Related Art
Roof and wall support is vital in mining and tunnelling operations. Mine and tunnel walls and roofs consist of rock strata, which must be reinforced to prevent the possibility of collapse. Rock bolts are widely used for consolidating the rock strata.
In conventional strata support systems, a bore is drilled into the rock by a drill rod, which is then removed and a rock bolt is then installed in the drilled hole and secured in place typically using a resin or cement based grout. The rock bolt is tensioned which allows consolidation of the strata by placing that strata in compression.
In some mining operations, the rock bolts are designed to be subsequently extracted by the mining equipment on extraction of the surrounding strata. These operations are common in coal mining using longwall or continuous mining operations. In these operations, large blocks of coal referred to as “panels” are accessed as ribs or walls and are extracted in a single continuous operation by mechanical cutting equipment such as longwall shearers and continuous miners. In establishing access to the panels, rock bolts are driven into the coal bed to bind the strata together and these rock bolts are subsequently extracted on extraction of the panels.
In the past, various types of rock bolts have been used in such operations. One common type of rock bolt is formed from a solid steel rod. These rock bolts exhibit very good support characteristics for the rib or wall but they have been known to tear conveyor belts or block transfer points as the extracted rock bolt is conveyed with the extracted coal. A lot of deeper mines using steel rock bolts have to modify their transfer points and place additional magnets on the conveyors to pick all the steel out of the coal. Nevertheless, many mines which are set up for steel bolts still experience downtime due to damage as a result of the extracted rock bolt.
Alternative types of rock bolts have been used to try to ameliorate this problem. This includes bolts made from other materials such as reinforced fibreglass or plastic. These bolts have the benefit that the plastic or the fibreglass will float during the normal coal washing process and as such do not contaminate the end product and typically do not damage the reinforced rubber conveyor belt used to transport the coal out of the mine. The problem with such bolts is that they typically have very low strength characteristics particularly in respect of shear and torsional strength.